14. The Autonomic Nervous System

Neuropeptides that act as natural opiates include

a. Substance P

b. Somatostatin and cholecystokinin

c. Tachykinins

d. Enkephalins

Receptors that bind acetylcholine at the postsynaptic membrane are:

(a) Chemically gated channels

(b) Voltage-gated channels

(c) Passive channels

(d) Mechanically gated channels

Since at any moment a neuron is likely to have thousands of neurons releasing neurotransmitters at its surface, how is neuronal activity (to fire or not to fire) determined?

In the Netherlands a young man named Jan was admitted to the emergency room. He and his friends had been to a rave. His friends say he started twitching and having muscle spasms which progressed until he was 'stiff as a board.' On examination, staff found a marked increase in muscle tone and hyperreflexia involving facial and limb muscles. In his pocket, he had unmarked dark yellow tablets with dark flecks. Analysis of the tablets showed them to contain a mixture of ecstasy and strychnine. Ecstasy would not cause this clinical picture, but strychnine, which blocks glycine receptors, could. Explain how.

The drug neostigmine blocks the activity of the enzyme acetylcholinesterase in the synaptic cleft. Predict the effects of this drug.

The poison curare (kyoo-RAH-ray) blocks the binding of acetylcholine to its receptors at the neuromuscular junction. What effects would you predict from such a poison? Can you think of any useful applications for it? Why might an overdose of it be lethal?

Match the following neurotransmitters with their correct description.    

_____ GABA    

_____ Dopamine     

_____ Substance P     

_____ Acetylcholine    

_____ Glutamate     

_____ Endorphins     

_____ Norepinephrine

a. Neuropeptide involved in transmission of pain

b. Neurotransmitter released at the neuromuscular junction

c. Major excitatory neurotransmitter in the brain

d. Major inhibitory neurotransmitter in the brain

e. Neuropeptide involved in relief of pain

f. Catecholamine involved in the autonomic nervous system

g. Catecholamine involved in movement and behavior

Which neurotransmitter(s) is/are used by sympathetic postganglionic neurons?

a. Epinephrine

b. Norepinephrine

c. Acetylcholine

d. Both a and b

e. All of the above

Many chemical warfare agents, such as the poisonous gas sarin, block the enzyme acetylcholinesterase in the synaptic cleft. What effects will this poison have on muscle contraction? What effects will it have on the autonomic nervous system? What symptoms would you expect to see from this poison?

Mrs. Jones has had a progressive decline in her mental capabilities in the last five or six years. At first her family attributed her occasional memory lapses, confusion, and agitation to grief over her husband's death six years earlier. When examined, Mrs. Jones was aware of her cognitive problems and was shown to have an IQ score approximately 30 points less than would be predicted by her work history. A CT scan showed diffuse cerebral atrophy. The physician prescribed an acetylcholinesterase inhibitor and Mrs. Jones showed slight improvement. What is Mrs. Jones's problem? Why did the acetylcholinesterase inhibitor help?

Biogenic amine neurotransmitters include all but

a. Norepinephrine

b. Acetylcholine

c. Dopamine

d. Serotonin

Inhibition of acetylcholinesterase by poisoning blocks neurotransmission at the neuromuscular junction because

a. ACh is no longer released by the presynaptic terminal.

b. ACh synthesis in the presynaptic terminal is blocked.

c. ACh is not degraded, so prolonged depolarization is enforced on the postsynaptic cell.

d. ACh is blocked from attaching to the postsynaptic ACh receptors.

The effects of neurotransmitter binding are very brief. Explain.